Talbot interference uses an interference of electromagnetic waves having various wavelengths including light or an X-ray to measure a form or composition of a subject. Generally, Talbot interference uses an imaging apparatus including an electromagnetic wave source, a diffraction grating, and a detector. The principle of Talbot interference will be described briefly. First of all, incident waves having a phase wavefront, that is, coherent incident waves are irradiated from an electromagnetic source to a subject. The electromagnetic waves through the subject changes their wavefront in accordance with the form or composition of the subject. When the electromagnetic waves having the wavefront change are diffracted by a diffraction grating, an interference pattern is formed at a position away from the diffraction grating by a specific distance called a Talbot distance. The interference pattern is detected and analyzed by a detector so that the phase wavefront (hereinafter, called a phase image) changed by the subject or the differential image of the phase wavefronts (hereinafter, called a differential image) may be acquired.
As disclosed in PTL 1, a shield grating (hereafter, called absorption grating) having a transmitting unit which allows electromagnetic waves to pass through and a shielding unit which shields electromagnetic waves at predetermined periods may be placed at a position where an interference pattern occurs to form a moire. The moire may be detected and analyzed to acquire the phase image or differential image of the subject. According to this method, a detector may be used which has a larger spatial resolution than the period of the interference pattern. For that reason, the method is often used in imaging apparatus according to Talbot interference using an X-ray as the electromagnetic waves (hereinafter, called an X-ray Talbot interference).
In a Talbot interferometer which uses an absorption grating to form a moire and detects the intensity distribution of the moire, the attitude of the diffraction grating or the absorption grating suitable for imaging depends on the wavelength of the electromagnetic waves to be used or the pitch of the diffraction grating or absorption grating. When the attitude of the diffraction grating or absorption grating is displaced from the attitude suitable for imaging, the noise ratio to the acquired phase image or differential image of the subject increases, which then may deteriorate the image quality.